Hydrostatic transaxles

ABSTRACT

An axle assembly for use in lawn tractors, pedestrian walk-behind mowers and snow blowers in the form of a housing having an internally disposed hydrostatic transmission and speed reducing gearing. An input shaft supported in the housing for driving a variable-displacement hydraulic pump of the hydrostatic transmission, the pump fluidly coupled to a fixed-displacement hydraulic motor of the hydrostatic transmission, and where the motor is drivingly connected through the speed reducing gearing to an output axle shaft or shafts. A mechanical differential disposed within said housing for applications requiring differential speeds of said axle output shafts. The housing being formed by three housing members and joined together along a substantially planar and horizontally peripheral seam formed therebetween such that two of said housing members are to one side of said seam and join with the third housing element. Two internal chambers formed by the three housing elements where one chamber contains the hydrostatic transmission and the other chamber contains the speed reducing gearing. A connecting shaft spanning between the chambers to provide the power transmission link between the hydrostatic transmission and the speed reducing gearing.

[0001] This invention relates to hydrostatic transaxles which are nowused in increasing numbers for lawn care and other outdoor duties as thepreferred choice for power transmission drive lines in products such aslawn and garden tractors, pedestrian walk-behind mowers and snowblowers.

[0002] Hydrostatic transaxles of the type currently sold in themarketplace require careful assembly and service practices in order toavoid certain problems occurring that may result in lower than expectedoperational life of the product. Hydrostatic transmissions operate mosteffectively and efficiently when they are constructed with exceedinglysmall clearances between their reciprocating and sliding elements. Thetransmission of power by such hydrostatic transmissions has now becomewidespread and the attendant small fluid leakage loss from the internalpressurized circuit during operation which is inherent with this type ofspeed changing device is generally considered insignificant as theresulting retardation in vehicle speed most often goes largely unnoticedby the end user. Hydrostatic transmissions work well and have a long anduseful life so long as the level of contamination suspended in the powertransmission fluid remains low. High levels of contamination carried bythe power transmitting fluid can rapidly wear out the aforementionedfine clearances resulting in an increase in fluid leakage, especiallyduring high pressure operation.

[0003] It is therefore of paramount importance during both the initialassembly process when the hydrostatic transaxle is built as well as atsubsequent service repair intervals, that the possibility ofcontamination entering the hydrostatic transmission and its surroundingfluid chamber be minimised. In simple terms, the chance for thehydrostatic transmission components being contaminated during handlingon the assembly lines in the factory recede as the number of componentsin the total assembly build is reduced. It follows therefore, that ifthe hydrostatic transmission could be fully assembled and sealed in thehousing prior to the reduction gearing and differential shaft componentsbeing added, there would be an advantage.

[0004] In the past, because hydrostatic transmissions were of theself-contained “bolt-on” type designed specifically to be fitted to aninterface provided on an exterior mounting face of a separate transaxlecontaining the reduction gear train, the possibility of contaminationentering the hydrostatic transmission was not an issue when some form ofa repair was needed in the separate transaxle drive train unit. Forexample, in the event that the hydrostatic transmission needed to bereplaced, this type of repair could be quickly undertaken just byremoving a few bolts in order to separate the unit from the transaxleand replace it with another unit. If on the other hand, a bearing orshaft seal needed to be replaced in the transaxle drive train, such arepair could be easily effected just by dis-assembly of the transaxleand without disturbing the internal components of the hydrostatictransmission which would stay in-place in their own housing. A typicaldesign of the so-called “bolt-on” self-contained “stand-alone” type ofhydrostatic unit for mating to a separate transaxle device is shown inEaton Corporation U.S. Pat. No. 5,234,321 incorporated herein asreference.

[0005] Due to improvement in the art during the past decade or so, thevast majority of hydrostatic transmissions now in use are of theintegrated type whereby a common housing is used to surround both thehydrostatic elements as well as the speed reducing gearing (anddifferential when required), typically as shown in FIGS. 3 through 5 inThoma et al. U.S. Pat. No. 4,979,583 incorporated herein as reference.Although the improvement of the “integrated” type over the earlier“bolt-on stand-alone” type of hydrostatic transmission and transaxlecombination has provided significant economic benefits in terms oflowering manufacturing cost of the drive line such that hydrostatictransmissions are now better able to compete more effectively withmechanical-shift gear transmissions, inconveniences can arise whenrepairs are needed. The consequence of shipping units back to thefactory for repair is both costly and inconvenient for the vehicleowner.

[0006] Furthermore, in the event of a service agent electing to make therepair himself, for example, a normally relatively simple repairinvolving the replacement of a worn bearing or seal, it is at present afact that this would first necessitate the splitting open of thetransaxle housing in order to gain access to those elements needingreplacement. As such action results in the hydrostatic transmissioncomponents being exposed to what may well be a relatively uncleanworking environment, a distinct possibility exists that the hydrostatictransmission might have become contaminated such the repair is onlyshort lived. Consequently, the service agent may elect to substitute thefaulty unit with a brand new replacement but this has the disadvantageof much additional expense for the vehicle owner, especially if theexisting hydrostatic transmission or conversely, the original gear traincomponents were considered by the agent to be in good and still usablecondition. There therefore is a need in the art for a new integratedhydrostatic transaxle that will allow simple repairs to be undertaken bythe dealership on the non-hydrostatic components without exposing theinternally disposed hydrostatic transmission components tocontamination.

[0007] With all known integrated hydrostatic transaxles currently sold,factory testing can only take place once the transaxle is fullyassembled as the hydrostatic portion as well as the geared portion arecontained within a surrounding two-piece housing structure. In the eventthe factory test indicates that the hydrostatic transmission is notoperating satisfactorily, repair and rectification can be both costlyand time consuming as the complete housing must first be dismantled inorder to be able to replace deficient hydrostatic componentry. What istherefore needed in the art a new form of integrated hydrostatictransaxle in which the two types of power transmitting componentrywithin the complete product package are separate from each other suchthat the hydrostatic transmission can be tested and approved before theremaining non-hydrostatic components are assembled in place. What isalso needed is a new form of integrated hydrostatic transaxle allowingrectification work, when needed, to be speeded up and therefore moreeconomic to perform. What is further needed is a new solution wherebythe amount of handing required during assembly on the assembly lines isminimised before the hydrostatic transmission is fully sealed within thesurrounding housing structure.

[0008] As integrated hydrostatic transaxles of the type currentlyavailable in the market require a large housing structure for containingboth hydrostatic and non-hydrostatic components, the machine toolsneeded to perform finish machining operations on the housing areexpensive due to their size. There would be a saving in machine toolinginvestment if the size of transaxle housing were smaller in size, andthere would be further saving in terms of economies of scale if one partof the housing structure of the hydrostatic transaxle could be used fornumerous other product types. What is therefore needed is a new form ofintegrated hydrostatic transaxle having a relatively small housingcomponent requiring machining for the mounting of the hydrostatictransmission such that the remaining and larger housing members requiredfor completion of the transaxle housing structure can be used in theiras-received die-cast condition. What is further needed is a universalcover housing element for the mounting of the hydrostatic transmissionsuch that the sub-assembly can be used in combination with any number ofdifferent case housing elements to satisfy a range of products types.

SUMMARY OF THE INVENTION

[0009] From one aspect the invention consists in a housing structure fora hydrostatic transaxle where the housing construction comprising threehousing elements that inter-relate to form separate chambers for thehydrostatic transmission components and the geared components. An inputshaft is supported in the housing and extends into the chambercontaining the hydrostatic transmission to drive the hydraulic pump. Anoutput shaft is also supported in the housing and extends into thatchamber containing the geared components. In instances when a mechanicaldifferential is also located within the chamber containing the gearedcomponents, the output shaft then comprises two shafts that extend fromthe differential in opposite directions. Within the chamber containingthe geared components, the output shaft or shafts is drivingly engagedto the speed reduction gears and where the gears are driven by aconnecting shaft that forms the power transmitting link between thehydraulic motor in the hydrostatic chamber and the geared components inthe gear chamber.

[0010] By this invention, the hydrostatic transmission components forthe hydrostatic transaxle can be assembled in a clean room and testedbefore the complete sub-assembly containing the hydrostatic transmissionis dispatched to another location where the non-hydrostatic componentsare added. As the hydrostatic sub-assembly is sealed by the surroundinghousing before entering the final assembly production lines, there is nochance for the hydrostatic transmission to become contaminated when theremaining components are added. In instances when the transaxlemanufacturer elects to sub-contract the task of building the completehydrostatic transmission to an outside agency, the supplied hydrostaticsub-assembly can be received in a ready-to-use condition therebyavoiding any need for the transaxle manufacturer to undertake inspectionprocedures to ascertain that the received goods are free fromcontamination from shipping and handling.

[0011] It is therefore an object of the invention to provide an improvedhousing for a hydrostatic transaxle whereby the chamber for thehydrostatic transmission components is segregated from that chambercontaining the speed reducing geared components in a manner whereby thehydrostatic transmission can be tested and approved before the remainingassembly involving the geared components takes place. It is a furtherobject of the invention to provide an improved housing for a hydrostatictransaxle whereby the service life of the unit can be extended byallowing simple repairs to be effected in the field without disturbanceor disassembly of the hydrostatic transmission components.

[0012] What is further needed in the art is a new form of integratedhydrostatic transaxle in which a relatively small housing componentstructured for carrying the hydrostatic transmission be provided with anability to resist and absorb within its structure the fluid pressuregenerated loads by the hydrostatic transmission such that the remainingand larger housing members of the hydrostatic transaxle serve to supportthe non-hydrostatic loads. It is a further object of the invention togroup all the machining operations for the housing structure of thehydrostatic transaxle into said smallest of the three housing elementsthereby providing material saving in tooling investment and totalmachining hours required.

[0013] It is a further object of the invention to segregate thehydrostatic transmission from the reduction gearing by providing a casehousing element with a substantially planar and horizontally peripheralseam serving as an abutment surface onto which interface two smallersized container-shaped housing elements whereby the power transmissionlink connecting the hydrostatic transmission to the reduction gearinghas an axis of rotation arranged in parallel relationship with regard tothe seam and where the housing elements serve to protect the powertransmission link from corrosion or falling debris such as grasschippings which commonly accumulate on the exterior surface ofhydrostatic transaxle apparatus.

[0014] In one form thereof, the hydrostatic transaxle of the inventioncomprises an axle assembly having a housing including first, second andthird housing elements joined along a substantially planar andhorizontally peripheral seam formed therebetween such that the first andsecond housing elements are to one side of the seam; the third housingelement being provided with first and second cavities and where thefirst cavity is closed by an opposite cavity provided by the firsthousing element to define a first chamber. The second cavity is closedby an opposite cavity provided by the second housing element to define asecond chamber; a hydrostatic transmission comprising avariable-displacement pump and fixed-displacement motor disposed withinthe first chamber and speed reducing gearing disposed within the secondchamber; at least one outwardly extending output power transmissionshaft rotatably mounted in the housing and an input power transmissionshaft rotatably mounted in the housing and operatively connected to thepump, the hydraulic motor being operatively connected to the outputpower transmission shaft by means of the speed reducing gearing, andwhere a connecting shaft spans across from the first chamber to enterthe second chambers to provide the power transmission link between thehydrostatic transmission and the speed reducing gearing.

[0015] Although the preferred shaft mounting location shown in thisinvention for the mechanical drive connection from the hydraulic motorto the projecting axle output is disposed along the seam whereby allthree housing elements provide support surfaces in the form ofsemi-cylindrical pockets, an alternative embodiment is disclosed wherebysuch support surfaces are disposed fully to one side of the seam. Anadvantage of this alternative embodiment is that it allows at least oneof the three housing elements to have a substantially flat profile atthe peripheral seam, for instance the gear housing element, and wherethis housing element may manufactured in various materials such as analuminium alloy casting; a pressed-steel component or as a simpleplastic or nylon moulding.

[0016] In the embodiments described below, the fluid pressure generatedloads by the hydrostatic transmission are easily absorbed and containedwithin the smallest of the three housing elements while the powertransmission link between the hydraulic motor in the hydrostatic chamberand the geared components in the gear chamber provide hithertounattainable improvements and savings in terms of assembly and repairpractices over the integrated hydrostatic transaxles types presently onthe market.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above mentioned and other novel features and objects of theinvention, and the manner of attaining them, may be performed in variousways and will now be described by way of examples with reference to theaccompanying drawings, in which:

[0018]FIG. 1 is a part-sectioned side view of the transaxle according tothe invention.

[0019]FIG. 2 is a plan view of the case element along the section lineI-I of FIG. 1.

[0020]FIG. 3 is a view of the hydrostatic transmission as it is mountedin the transmission cover element according to the invention.

[0021]FIG. 4 is a view of the transmission cover element and hydrostatictransmission along the section line II-II of FIG. 4.

[0022]FIG. 5 is a view of the hydrostatic transmission located withinthe internal chamber formed between the case and the transmission coverelement.

[0023]FIG. 6 is a view of the hydrostatic transmission and a portion ofthe gear reduction located within their respective internal chambersformed between the case and the transmission cover element.

[0024]FIG. 7 is a plan view of the gear cover element showing itsinterior details.

[0025]FIG. 8 is a view of the hydrostatic transaxle according to afurther embodiment of the invention.

[0026]FIG. 9 is a side view of the hydrostatic transaxle along thesection line III-III of FIG. 8.

[0027]FIG. 10 is a plan interior view of the gear cover element of FIGS.8 and 9.

[0028]FIG. 11 shows an alternative mounting arrangement on the case forfixing the hydrostatic transaxle to a frame or chassis.

[0029] The housing for the hydrostatic transaxle 1 can be comprised ofat least three housing elements, the main housing element being herecalled the case 2, the largest of the three housing elements beingprovided with a mounting face 3 and which surrounds two cavities 4, 5sunken from the surface. The first cavity 4 provides internal space forthe location of the hydrostatic transmission 7 whereas the second cavity5 provides the space for the location for various elements comprisingthe speed reducing gearing 6 and mechanical differential 8. A number ofsemi-circular pockets are also provided on the mounting face to supportvarious shafts and bearings, for instance, pockets 10, 11 for the outputtransmission shaft, which as shown here comprise two output axletransmission shafts 12, 13.

[0030] A transmission cover element 15 and a gearing cover element 16are attached against the case 2 on this mounting face 3, these covers15, 16 being attached to the case 2 by screws or bolts. For instance,shown are a series of holes 17 on mounting face 3 of case 2 which arearranged to surround first cavity 4 into which screws 20 engage. Asecond series of holes 18 are also included on mounting face 3 of case 3which are arranged to surround second cavity 5 into which screws 21engage. All such holes 17, 18 are preferably cast as slightly taperedblind holes so that self-threading screws are used transmission coverelement 15 and geared cover elements 16 respectively to the case 2.

[0031] The mounting face 3 on case 2 is the horizontal peripheral seamthat surrounds both the first and second cavities 4, 5 and where, inthis first embodiment, the axle output transmission shafts 12, 13 havetheir axis of rotation substantially coincident with the seam. Thetransmission cover element 15 and gear cover elements 16 abut againstthe seam/mounting face 3 of the case 2 along a parting plane as shown inFIG. 1.

[0032] As shown in FIGS. 1 and 3, the shape of the transmission coverelement 15 is substantially in the form of a container such that it hasa cavity 25 into which a portion of the hydrostatic transmission 7extends into, and where a number of mounting surfaces are included, suchas shown as bosses 26, 27 to which part of the hydrostatic transmission7 can be attached. Preferably, the hydrostatic transmission is mountedto the cover element 15 rather than to the case element 2 to obtainmaximum benefit of this invention, although it could also possible tomount some or all of the hydrostatic transmission components in the case2, and possibly then the input shaft driving the pump of the hydrostatictransmission would be supported by bearings provided in the case element2.

[0033] As shown, at the open-end of the container of transmission coverelement 15, a surrounding radially outwardly extending base flange 28 isprovided and where a plurality of holes 29 are included on this flangeor lip 28 so that attachment screws 20 can pass through holes 29 andextend beyond its mounting surface 30 and engage with holes 17 providedon the case 2 that surround the first cavity 4. The bottom surface offlange 28 is therefore the mounting surface 30 of the transmission coverelement 15 which interfaces with the mounting surface 3 provided on thecase 2. At this interface, sealing compound of the anaerobic type isused on the interface so that the internal chamber 33 which is formed bycavities 4, 25 in the case 2 and transmission cover element 15respectively, into which is housed the hydrostatic transmission 7 andits operating fluid, is separated and protected from the outer exteriorenvironment of the transaxle 1. Internal chamber 33 is flooded withhydraulic fluid which acts as the power transmitting medium for thehydraulic pump 35 and motor 36 of the hydrostatic transmission 7, andwhere chamber 33 is connected by passage 38 in the vertical wall 39 oftransmission cover element 15 so that expansion and contraction of thefluid volume in chamber 33 can take place by spilling the excess amountinto an auxiliary chamber 40 provided by header tank 41 here shownattached to the transmission cover element 15.

[0034] As best shown in FIG. 2, cavity 5 in case element 2 is providedwith a number of semi-cylindrical pockets 51, 52, 53, 54 to carry anumber of bearings which provide the support for shafts 60, 61 on whichvarious elements of the speed reduction gear train 6 are mounted.Further pockets 203, 204 are provided in case element 2 for thepositioning of bearing 191 and seal 193 respectively as shown in FIGS. 5and 6. The shape of the gear cover element 16 is also generally in theform of a container. FIG. 7 being a plan view and shows it havingseveral semi-cylindrical pockets such as pockets 63, 64 that correspondwith pockets 51, 52 in case 2, whereas pockets 66, 67 for intermediaryshaft 61 correspond with pockets 53, 54 in case 2. Pockets 68, 69 foraxle output shafts 12, 13 correspond with pockets 10, 11 in the case 2,and where bearings 70, 71 are used to support respective shafts 12, 13.

[0035] As best seen in FIGS. 1 and 7, surrounding cavity 50 of coverelement 16 at the mounting surface 74 is an outwardly radially extendingflange 75 where a plurality of holes 77 are included on flange 75allowing attachment screws 21 to pass through and engage with theircorresponding holes 18 provided in case 2 that surround the secondcavity 5. The bottom of the flange is therefore the mounting surface ofthe gear cover element which interfaces with the mounting surfaceprovided in the case 2. At this interface, sealing compound is use sothat the internal chamber 80 created by the second cavity 5 in the case2 and the cavity 50 in the gear cover element 16 is isolated from theexterior of the transaxle 1.

[0036] The hydrostatic transmission 7 used to best illustrate theadvantages of this invention is preferably mounted to the transmissioncover element 15 prior to that element being attached to the case 2. Aninput shaft supported by bearings 101, 102 in the transmission coverelement 15 is operatively connected to the pump of the hydrostatictransaxle 1, and where a rotary shaft seal 103 is fitted about the inputshaft 100 is prevent fluid from chamber 33 escaping. Although the inputshaft 100 could be arranged to directly drive the pump 35 if so desiredor alternatively, input shaft 100 can be operatively connected to thepump 35 by means of gears which may be of the bevel type as is shown orspur gears. Bevel pinion 107 is fixed to shaft 100 and meshes with bevelgear 108 to drive the cylinder-barrel 110 of the pump 35. Bevel gear 108is fixed to cylinder-barrel 110 of the pump so to rotate at equal speed,and where the barrel 110 is supported for rotation on pintle-valve 112,pintle-valve 112 being provided with internal fluid passages 113, 114 sothat fluid from barrel 110 can flow to the cylinder-barrel 115 of thehydraulic motor 36.

[0037] Although the form of hydrostatic transmission here used todescribe the invention is of a type using a radial array of cylindricalrollers, other forms of fluid displacement machines may also be used,for example, those having pistons with slippers or even ball pistons.Furthermore, the hydrostatic transmission as here described has a pumpand motor arranged in co-axial back-to-back relationship, but ahydraulic right-angle fluid connection could also be used in which therotational axes of the pump and motor is perpendicular, and therebyremoving the need to include bevel gearing.

[0038] Barrel 110 of the pump 35 is provided with a plurality ofradially arranged cylinders 117 which are a fixed axial distancerelative to the arcuate shaped slots 118, 120 provided on thepintle-valve 112. Each cylinder 117 includes a port 119 which matcheswith arcuate slots 118, 120 during rotation of barrel 110. Each cylinder117 receives a piston 122 to which a roller 123 is mounted on its outerend and where the rollers 123 operate against a surrounding annulartrack-ring 125. The barrel 115 of the hydraulic motor 36 is likewiseprovided with a plurality of cylinders 126 which are a fixed axialdistance relative to the arcuate shaped slots 127, 128 provided on thepintle-valve 112. Each cylinder 126 includes a port 130 which matcheswith arcuate slots 127, 128 during rotation of barrel 115, and eachcylinder 126 receives a piston 131 and a roller 132 is mounted on theouter end of each piston 131 and where the rollers 132 operate against asurrounding annular track-ring 133. In the case of the hydraulic motor36, track-ring 133 is eccentrically positioned with respect to thepintle-valve 112 whereas in the case of the hydraulic pump 35,track-ring 125 is pivotable about pivot pin 135. Control-shaft 136 isconnected to track-ring 125 by link pins 138, 139 in order that theeccentricity of track-ring 125 can be varied relative to thelongitudinal axis of the pintle-valve 112.

[0039] The control shaft 136 is supported between a pair ofsemi-cylindrical pockets 140, 141 provided on the mounting surface 30 ofthe transmission cover element 15 and a complementary pair of pockets142, 143 provided on the mounting surface 3 of the case 2. A rotary seal145 is positioned within a further pair of pockets 146, 147 to surroundcontrol-shaft 136 and prevent the escape of hydraulic fluid frominternal chamber 33.

[0040] As shown in FIG. 1, in the interior cavity 25 of the transmissioncover element 15, inwardly projecting bosses 26, 27 mounting are spotfaced in order to provide a datum and thereby an accurate mountingsurface for the hydrostatic transmission 7. During the same machiningoperation, the vertical hole 153 is sized for both the shaft bearings101, 102 and fluid seal 103.

[0041] Located in the space between the barrels 110, 115, thepintle-valve 112 and pivot pin 135 are clamped between a two-piecesub-frame 160, 161 which can then be attached by screws 162 to themachined mounting surfaces on the bosses 26, 27. Holes or slots (notshown) in both sub-frame elements 160, 161 allow the passage of thesefastening screws 162 which are received into threaded holes providedwithin the bosses 26, 27 in the transmission cover element 15. When thesub-frame 160, 161 is located onto bosses 26, 27, the action oftightening screws 162 results that sub-frame elements 160, 161 arepressed together while at the same time clamping the pintle-valve 112and pivot pin 135 in place such that the hydrostatic transmission isfixedly secured against the mounting surface provided in transmissioncover element 15.

[0042] A second sub-frame 165 in the form of a pressed steel “L” shapedplate may also be used to secure the hydrostatic transmission to thetransmission cover element 15 as shown in FIGS. 3 and 4. One arm shownas 166 of sub-frame 165 is provided with an aperture 167 through whichthe end of the pintle-valve 112 protrudes through. That portion at endof the pintle-valve 112 which is inserted through aperture 167 mightvery well be ground with an outer profile conducive to causing thematerial of arm 166 adjacent to aperture 167 to deform slightly as theend of the pintle-valve is passed through before deforming back to holdtight when it reaches the correct resting place on the pintle-valve.Likewise, a further aperture 169 is included through which the pivot pin135 protrudes through. The arm or base 170 of sub-frame 165 is providedwith two holes (not shown) through which fastening screws 174 passthrough, and where the base 170 rests on a machined surface 175 on theinterior of the transmission cover element 15. Once screws 174 aretightened, base 170 is fastened to mounting surface 175 and thus,sub-frame 165 and hydrostatic transmission becomes fixedly held to thetransmission cover element 15.

[0043] As shown in FIG. 4, motor track-ring 133 is attached to thecentral sub-frame 160, 161 by way of pins 180, 181 that extend from endface 182 of track-ring 133 and engage between respective pairs ofpockets shown by dotted lines 184, 185 provided on the interface betweensub-frame elements 160, 161. The pins 180, 181 and thereby track-ring133 become locked in position once screws 162 holding the sub-fame 160,161 to the mounting surface bosses 26, 27 are tightened.

[0044] Therefore, once both sub-frames 160, 161, 165 are fastened totransmission cover element 15, the hydrostatic transmission 7 held inposition within chamber 33.

[0045] The shaft 190 connecting with the hydraulic motor 36 is built-upas a sub-assembly with its support bearings 191, 192 and seal 193, andwhere a drive coupling 195 is used top connect shaft 190 to motor barrel115. Anaerobic sealant is applied on the surfaces of semi-cylindricalpockets 200, 201, 202 in the transmission cover element 15 before theshaft sub-assembly is moved into position in element 15.

[0046] The transmission cover element 15 with its attached hydrostatictransmission 7 is then lowered over cavity 4 in the case 2 as shown inFIG. 5. The mounting surface 3 on the case 2 has anaerobic sealingcompound applied, and once in place, the series of screws 20 passthrough the holes 29 of the radially extending flange 28 or lip to beengaged into holes 17 in case 2 so that case 2 and cover 15 are tiedtogether as a unitary housing structure. Thus the complete hydrostaticsub-assembly is complete and ready to be tested once transmission fluidhas been poured into the internal chamber 33. Once the test is over, thehydrostatic sub-assembly is ready for dispatch so that the remaininggear and other components can be added before the gear cover element 16and case 2 are locked together by screws 21.

[0047] A mechanical disengage mechanism is sometimes useful inhydrostatic -transaxles when it is desired to manually push the vehiclewithout operating the engine that is normally is used to drive thetransaxle and propel the vehicle. As here disclosed, this can be easilyachieved by having a gear 211 fixedly mounted to a brake shaft 60 inorder that a mechanical disengage mechanism can be incorporated betweenshafts 190, 60.

[0048] A collar element 212 is used to connect respective shafts 190, 60together by means of spline connections 213, 214. Lever means (notshown) act in groove 215 on collar element 212 to shift the collarslightly to the left so that the spline 213 connection is no-longerengaged to motor shaft 190 so that shafts 190, 60 are no-longerconnected together to rotate at equal speed. A parking brake 217attached to shaft 60 ensures the vehicle can be arrested during periodswhen shafts 190, 60 remain disconnected. Shaft 60 is supported in abearing 220 seated between semi-cylindrical pockets 52, 64 provided incase 2 and gear cover element 16 respectively, and also journalled atits inner end 225 in a hollow 226 provided in shaft 190.

[0049] However, it should be noted that if no mechanical disengage isrequired, or when an alternative method is used to obtain the sameeffect, for instance, through the incorporation of a mechanism wherebythe fluid in the hydrostatic fluid circuit between the pump and motor isshort-circuited, there would be no need to use two shafts such as 60,190. Instead, a single shaft could be used which would connect thecylinder barrel 115 of the motor 36 to the pinion gear 211 so that poweris transmitted from the barrel 115 to the gear 211. In either casehowever, the shaft or shafts connecting the hydraulic motor 36 to thegear reduction train 6 for the purposes of definition for this inventionis called the power transmission link.

[0050] Prior to the assembly into the case 2 of the non-hydrostaticelements such as shaft 60, anaerobic sealing compound is applied to themounting surface 3 as well as to all the semi-cylindrical pockets suchas pocket 52. Thus then all the remaining components such as brake-shaftsub-assembly, speed reducing gearing and the differential (when used)together with the output axle shaft or shafts can be lowered intoposition in the case 2. As depicted, the speed reducing gearing 6comprises a pinion gear 211 splined 228 to brake shaft 60 which mesheswith a gear 230 fixed on an intermediate shaft 61. Intermediate shaft 61has a further gear 231 fixed to it which meshes with the ring gear 233that comprises as shown part of the differential unit 8. Thedifferential 8 shown is of the type that has four bevel gears 235, 236,237, 238, two of which 236, 238 are attached to respective axle outputshafts 12, 13 that extend out from the chamber 80. For thoseapplications where there is no requirement to have a differentialeffect, shafts 12, 13 would in effect be a single shaft. Gear 233 wouldbe modified so to omit bevel gears 235, 236, 237, 238 and be fixed tothe output shaft. The output shaft would still protrude from the case 2and cover 15 on both sides or only on one side to suit the application.

[0051] As shown in FIG. 2, bearings 240, 241 are provided for theintermediate shaft 61 which sit in pockets 53, 54 in case 2 and pockets66, 67 in gear cover element 16.

[0052] It is a feature of the invention that both cover elements 15, 16engage on the same bridging element, the example used to illustrate thisbeing cylindrical bearing member 192, this being accomplished bycylindrical bearing member 192 spanning the semi-cylindrical pockets202, 63 provided in the otherwise separate cover elements 15, 16. As aresult, motor shaft 190 and brake shaft 60 are not exposed to theexterior of the transaxie even though the pairs of cavities 4, 25 and 5,50 creating respective chambers 33, 80 for the hydrostatic transmission7 and speed reducing gearing 6 are separate from each other. It shouldbe noted however, especially for instance, were shafts 190, 60 combinedinto a single shaft, that a rotary seal member could perform as abridging element in place of a cylindrical bearing member. In thatmodification, the seal would ideally be pressed into a cylindricalsleeve, and where the sleeve would fit in pockets such as pocket 51 incase 2 and pockets 202, 63 in respective cover element 15, 16. Be thebridging element a seal or a bearing or just an empty sleeve, anaerobicsealant would be smeared at the interface where the bridging element isin engaging contact with the pockets in the housing so that externalmoisture or contamination is unable to enter chambers 80, 33. For easeand convenience, the outer profile for the bridging element best suitedto accomplish the task is cylindrical as depicted but the outer profilecould be modified, for instance to being square, and still work.

[0053] Therefore, whatever component is chosen to span the gap betweenthe two cover housing elements 15, 16 about the power transmission linkbetween the hydraulic motor portion and the gear portion of thehydrostatic transaxle, the advantage of being able to segregate chambers33 from 80 from each other as well as isolate said chambers from theexternal environment of the hydrostatic transaxle is intended to fallwithin the scope of the claims. Furthermore, it is also intended thatthis invention cover an arrangement whereby the power transmission linkspanning chambers 33, 80 is not protected by any bridging element atall, and where in that arrangement a portion of the connecting shaft orshafts comprising the power transmission link would be exposed to theouter environment of the hydrostatic transaxle. In that respect,provided two rotary seals are applied on the connecting shaft, each sealbeing located adjacent the interface between respective cover elementsand the case element, no contamination can enter chambers 5, 33. If theexposed portion of connecting shaft is lying downward in orientation,then debris and dust is unlikely to collect in the small gap that islikely to exist between the connecting shaft and housing.

[0054] Once all the gear train elements are in place, anaerobic sealingcompound is applied over those seal and bearing elements whichinter-relate with pockets provided in the gear cover element 16. Thengear cover element 16 is placed in position over the cavity 5 of thecase 2 before screws 21 are inserted through holes 77 to engage withblind holes 18. Once screws have been tightened, case 2 and gear cover16 elements are thus firmly together.

[0055] To operate the hydrostatic transaxle 1, when track-ring 125 ofthe pump 35 is moved by control-shaft 136 into an eccentric positionrelative to the pintle-valve 112, and during rotation of barrel 110 bythe input shaft 100, the pistons 122 reciprocate radially within theirrespective cylinders 117 and fluid inside the cylinders 117 is displacedthrough port 119 and flow takes place between arcuate shaped slots 118,120. The fluid in passages 113, 114 enters the motor 36 through arcuateshaped slots 127, 128 into cylinders 126 in barrel 115 by way of ports130. The fluid entering each cylinder 126 causes pistons 131 toreciprocate and through the relationship to the eccentrically positionedtrack-ring 133, and thereby barrel 115 is caused to rotate. Barrel 115being connected to shaft 190 by coupling 195 cause shafts 190, 60 of thepower transmission link to rotate at equal speed, and power istransmitted by gear 211 fixed to shaft 60 to the remaining elements ofthe speed reducing means 6 for the purpose of torque multiplication tothe transmission output shaft or axle shafts 12, 13.

[0056] In the second embodiment of the invention as shown in FIGS. 8 to10, the two main difference over what has already been described for thefirst embodiment is that the rotational axes of the power transmissionlink as well as the other shafts on the gear reduction compartment areno-longer coincident with the peripheral seam but are now lying offsetto one side of the seam; and secondly, the mounting surfaces provided inthe housing onto which the hydrostatic transmission components are fixedare now lying on the peripheral seam. The housing structure of thehydrostatic transaxle comprises a main housing case 251 and two smallerhousing cover elements, 252, 253. Cover element 252 includes themounting surfaces 270, 271 for attachment of the hydrostatictransmission components whereas gear cover element 253 is a form ablanking plate with protuberances where necessary.

[0057] The axle output shaft(s) 256 and the other shafts required forspeed reduction from the hydrostatic transmission such as the powertransmission link shafts 254, 255 are here shown located belowperipheral seam or parting-plane 2 50. In this respect, sub-surfacebearing carriers, here called inserts are needed such is shown in FIG. 9by way of example as insert 260. Insert 260 is fitted into a channel asshown 290 provided in the case element 251 and is arranged so that itstop surface 261 is level with the peripheral seam 250. The peripheralflat portion 291 of gear cover element 253 that lies directly above thetop surface 261 of insert 260 acts to lock and hold insert 260 in placewithin the channel 290.

[0058] Further inserts similar to the type 260 are used for shafts 254,255 and the intermediary shaft (not shown), shafts 255 being connectedto output shaft(s) 256 by the type of gearing already described for thefirst embodiment.

[0059] As shown in FIG. 8, various bearings and seals such as bearings273, 275, 276 and seals 274, 277 are located within respectivesemi-cylindrical pockets 280, 282, 283 and 281, 284 provided in the casehousing element 251. All these bearings and seals are positioned byinserts so that they are sunken from the surface of the parting-plane250 to lie in case element 251. For instance, insert 300 is provided forbearings 273, 275 and seal 274, and where the flat top surface 301 ofinsert 300 abuts with the flat junction surface 302 provided in thetransmission cover element 252. Inserts 305, 306 are similarly used, buthere they lie between the case element 251 and the flat portion 291 ofgear cover element 253.

[0060] The gear cover element 253 shown in FIG. 10 can be generally flatin profile about its peripheral seam 292 adjacent to where the mountingholes 293 are located, but includes a central cavity marked as 294 thatwhen viewed from the side, would be bulge shaped to provide thereby roomfor the various gears and differential that partially extend across theparting plane 250 into cavity 294 when elements 251, 253 become attachedtogether. Screws 296 are shown locking the peripheral flat portion 291of gear cover element 253 to the case element 251.

[0061] As the various shafts such as 254, 255, 256 are now locatedburied within the structure case element 251 and not withstanding thoseforces and loads tending in the direction towards the gear cover element291, the bulk of the mechanical loads are absorbed in the case element251. Therefore gear cover element 291 is subjected to less loads than inthe first embodiment such that for certain light-duty applications canbe manufactured as a simple and inexpensive steel pressing orplastic/nylon moulding to thereby, provide further worthwhile savings inthe overall manufactured cost of the hydrostatic transaxle.

[0062]FIG. 11 differs only very slightly from the hydrostatic transaxleshown in the previous embodiments of the invention in order to show thatthe case element 320 may have groups of upwardly extending externalmounting bosses 321 and 322 that extend above the gear cover element 323adjacent to respective axle output shafts 12, 13. All the bosses containa through-hole 325 so that the case element 320 can be bolted to theunderside frame or chassis of the vehicle.

[0063] For many applications, it is most advantageous that the inputshaft for the hydrostatic transaxle be located in the transmission coverelement as shown in the embodiment illustrated. However, should itbecome advantageous to locate the input shaft in what before wasdepicted as the case element, then the above described embodiments wouldbe adapted so that the hydrostatic transmission is attached to mountingsurfaces provided in the case rather then in the transmission coverelement. Equally, the hydrostatic transmission and geared componentscould each be located within two separate cavities provided in a singlecover housing element and where now two separate case elements would beused, one case element having a cavity for the hydrostatic transmissionand the other case element having a cavity for element having a cavityfor the geared components. With this re-arrangement of the housingparts, respective pairs of cavities combine to form chambers, onechamber for the hydrostatic transmission and another but distinctlyseparate chamber for the geared components. In all variations with thehousing construction, the power transmission link spanning that chambercontaining the hydrostatic transmission to the other chamber containingthe reduction gearing and differential would still be needed.

[0064] Although a radial piston hydrostatic transmission has beenillustrated for the purpose of describing this invention, an axialpiston hydrostatic transmission may also be used to good effect. In theaxial piston type of hydrostatic machine, the centre section thatcontains within it the fluid passages connecting the hydraulic pump tothe hydraulic motor, by incorporation with this invention be attached tothe transmission cover element is a similar manner as the sub-frameshere described for the radial piston embodiments. Alternatively, thecentre section could be attached near to the bottom surface of thecavity in a case element in a manner whereby a similar transmissioncover element and a geared cover element is used in combination with thecase as has already been described for the embodiments chosen to bestexplain the invention. As a further alternative, the axial pistonhydrostatic transmission may be mounted to the exposed surface on acover element having separate cavities for the hydrostatic transmissionand gearing elements. In this arrangement the center section would actas the transmission case element by enclosing the cavity in the cover tocreate the internal chamber for the hydrostatic transmission. In adesign having the axial piston form of hydrostatic transmission, itwould also be possible to mount the centre section or even theswash-plate of the pump directly adjacent to where the input drive shaftenters the housing structure of the hydrostatic transaxle. However, inall such variations, a power transmission link is required to connectthe motor of the hydrostatic transmission in the one chamber to thereduction gearing and differential located in the other chamber.

[0065] It is to be understood that while we have illustrated anddescribed various embodiments of our invention, it is not to be limitedto any one specific form or arrangement of parts herein described andshown except insofar as such limitations are included in the claims. Weclaim:

We claim as follows:
 1. An axle assembly comprising a hydrostatictransmission and a mechanical differential disposed adjacent one anotherin respective chambers formed by a surrounding housing structure, and abridging element disposed between said chambers, said housing structureincluding two housing cover elements arranged side by side and eachengaging a respective end of said bridging element, said hydrostatictransmission and said mechanical differential being operativelyinterconnected via reduction gearing disposed within said housingstructure, said bridging element surrounding and shielding a powertransmission link comprising at least one shaft passing from said firstchamber to said second chamber for the transmission of power betweensaid hydrostatic transmission and said mechanical differential.
 2. Anaxle assembly according to claim 1 wherein said bridging element has amale profile arranged for insertion into female pockets provided inrespective said housing cover elements.
 3. An axle assembly according toclaim 2 wherein said bridging element is cylindrical and where each ofsaid female pockets is semi-cylindrical in shape.
 4. An axle assemblyaccording to claim 3 wherein said bridging element further performs as abearing to support said at least one shaft.
 5. An axle assemblyaccording to claim 3 wherein said bridging element includes anintermediate portion and where said intermediate portion is exposedexteriorly of said housing structure.
 6. An axle assembly according toclaim 3 wherein said bridging element furthermore performs in the roleof bearing to support said at least one shaft and includes anintermediate portion, said intermediate portion being exposed exteriorlyof said housing structure.
 7. An axle assembly according to claim 1wherein said at least one shaft comprises a motor shaft and a brakeshaft and where the driving connection between said motor shaft and saidbrake shaft takes place in the second chamber.
 8. An axle assemblyaccording to claim 7 wherein said bridging element has a male profilearranged for insertion into female pockets provided in respective saidhousing cover elements, said bridging element includes an intermediateportion and where said intermediate portion is exposed exteriorly ofsaid housing structure.
 9. An axle assembly according to claim 8 whereinsaid bridging element is cylindrical in shape and registers respectivesaid housing cover elements together about the rotational axis of saidat least one shaft.
 10. An axle assembly according to claim 9 andincluding a pair of axle shafts rotatably supported in said housingstructure and wherein said housing cover elements are respectivelyprovided with substantially uniplanar junction seams meeting at aparting plane arranged to be coincident with the longitudinal axis ofsaid bridging element.
 11. An axle assembly according to claim 7 andincluding a parking brake external to said housing structure andattached to said brake shaft, a control shaft rotatably supported insaid housing structure for adjusting the fluid displacement of saidhydrostatic transmission, said bridging element including anintermediate portion and where said intermediate portion is exposedexteriorly of said housing structure and lies generally between saidparking brake on the one hand and said control shaft on the other hand.12. An axle assembly according to claim 11 and including a fluid barrierdisposed adjacent said bridging element in said housing structure toprevent hydraulic fluid held within said first chamber from enteringsaid second chamber, a header tank disposed external to said housingstructure and arranged to communicate with said first chamber to allowthe expansion and contraction in the fluid volume held by said firstchamber.
 13. An axle assembly according to claim 12 wherein saidhydrostatic transmission includes a pintle-valve or axial piston centersection equivalent and arranged to be fixidly mounted to saidhydrostatic transmission cover element.
 14. An axle assembly accordingto claim 13 and including a pair of axle shafts rotatably supported insaid housing structure and wherein said housing cover elements arerespectively provided with substantially uniplanar junction seamsmeeting at a parting plane arranged to be coincident with thelongitudinal axis of said bridging element.
 15. An axle assemblycomprising a hydrostatic transmission and a reduction gear traindisposed adjacent one another in respective chambers formed by asurrounding housing structure, and a bridging element disposed betweensaid chambers, said housing structure comprising at least three housingelements of which two are defined as being a hydrostatic transmissioncover element and a gearing cover element arranged side by side and eachengaging a respective end of said bridging element such that anintermediate portion of said bridging element is exposed exteriorly ofsaid housing structure, said bridging element surrounding and shieldinga power transmission link comprising at least one shaft passing fromsaid first chamber to said second chamber for the transmission of powerbetween said hydrostatic transmission and said reduction gear train. 16.An axle assembly according to claim 15 wherein said bridging element hasa male profile arranged for insertion into female pockets provided inhydrostatic transmission cover element and said gearing cover elementrespectively.
 17. An axle assembly according to claim 16 wherein saidbridging element is cylindrical and where each of said female pockets issemi-cylindrical in shape.
 18. An axle assembly according to claim 17wherein said bridging element further performs as a bearing to supportsaid at least one shaft.
 19. An axle assembly according to claim 18 andincluding a mechanical differential disposed in the same chambercontaining said reduction gear train, said hydrostatic transmission andsaid mechanical differential being operatively interconnected via saidreduction gear train.
 20. An axle assembly according to claim 19 andincluding a pair of axle shafts rotatably supported in said housingstructure and wherein said hydrostatic transmission cover element andsaid gearing cover element are respectively provided with substantiallyuniplanar junction seams meeting at a parting plane arranged to becoincident with the longitudinal axis of said bridging element.
 21. Anaxle assembly according to claim 20 and including a fluid barrierdisposed adjacent said bridging element in said housing structure toprevent hydraulic fluid held within said first chamber from enteringsaid second chamber, a header tank disposed external to said housingstructure and arranged to communicate with said first chamber, saidheader tank attached to said hydrostatic transmission cover element andallowing the expansion and contraction in the fluid volume held by saidfirst chamber.
 22. An axle assembly according to claim 21 wherein saidhydrostatic transmission includes a pintle-valve or axial piston centersection equivalent and arranged to be fixidly mounted to saidhydrostatic transmission cover element.
 23. An axle assembly comprisinga hydrostatic transmission and a reduction gear train disposed adjacentone another in respective chambers formed by a surrounding housingstructure, and a bridging element disposed between said chambers andhaving an intermediate portion positioned between two end portions andwhere said intermediate portion is exposed exteriorly of said housingstructure, said bridging element mounted in said housing structure suchthat one end portion lies nearer to the first chamber containing saidhydrostatic transmission while the other end portion lies nearer to thesecond chamber containing said reduction gear train, said bridgingelement surrounding and shielding a power transmission link comprisingat least one shaft passing from said first chamber to said secondchamber for the transmission of power between said hydrostatictransmission and said reduction gear train.
 24. An axle assemblyaccording to claim 23 and including a mechanical differential disposedin the same chamber containing said reduction gear train, saidhydrostatic transmission and said mechanical differential beingoperatively interconnected via said reduction gear train.
 25. An axleassembly according to claim 24 and including a pair of axle shaftsrotatably supported in said housing structure and where longitudinalaxis of said bridging element has a parallel alignment with respect tothe rotational axis of said axle shafts.
 26. An axle assembly accordingto claim 25 wherein said bridging element further performs as a bearingto support said at least one shaft.
 27. An axle assembly according toclaim 26 and including a parking brake external to said housingstructure and attached to said at least one shaft.
 28. An axle assemblyaccording to claim 27 and including a fluid barrier disposed adjacentsaid bridging element in said housing structure to prevent hydraulicfluid held within said first chamber from entering said second chamber,a header tank disposed external to said housing structure and arrangedto communicate with said first chamber, said header tank attached tosaid housing structure allowing the expansion and contraction in thefluid volume held by said first chamber.
 29. An axle assembly accordingto claim 24 wherein said housing structure is comprised of at leastthree housing elements and where a pair of axle shafts are rotatablysupported between two of said of at least three housing elements, saidaxle assembly including a parking brake external to said housingstructure and attached to said at least one shaft, a control shaftrotatably supported in said housing structure for adjusting the fluiddisplacement of said hydrostatic transmission, said bridging elementpositioned in said housing structure such that it lies generally betweensaid parking brake on the one hand and said control shaft on the otherhand.
 30. An axle assembly according to claim 23 wherein said axleassembly includes a mechanical differential and a pair of axle shafts.31. An axle assembly according to claim 30 where said mechanicaldifferential is disposed in the same chamber in which said reductiongear train is disposed
 32. An axle assembly according to claim 30 wheresaid axle shafts are rotatably supported in said housing structure anddrivingly connected to said mechanical differential.
 33. An axleassembly according to claim 32 wherein said housing structure iscomprised of at least three housing elements and where a pair of axleshafts are rotatably supported between two of said of at least threehousing elements, said axle assembly including a parking brake externalto said housing structure and attached to said at least one shaft, acontrol shaft rotatably supported in said housing structure foradjusting the fluid displacement of said hydrostatic transmission, saidbridging element positioned in said housing structure such that it liesgenerally between said parking brake on the one hand and said controlshaft on the other hand.
 34. An axle assembly according to claim 33wherein said bridging element furthermore performs in the role ofbearing to support said at least one shaft.
 35. An axle assemblycomprising a hydrostatic transmission and a reduction gear traindisposed adjacent one another in respective chambers formed by asurrounding housing structure, and a bridging element disposed betweensaid chambers, said housing structure including a hydrostatictransmission housing cover element engaging whichever end of saidbridging element is lying nearer to the first chamber containing saidhydrostatic transmission, said bridging element surrounding andshielding a power transmission link comprising at least one shaftpassing from said first chamber to said second chamber for thetransmission of power between said hydrostatic transmission and saidreduction gear train.
 36. An axle assembly according to claim 35 whereinsaid hydrostatic transmission housing cover element does not engage theend of said bridging element lying furtherest from said first chamber.37. An axle assembly according to claim 36 wherein said axle assemblyincludes a mechanical differential and a pair of axle shafts.
 38. Anaxle assembly according to claim 37 where said mechanical differentialis disposed in the same chamber in which said reduction gear train isdisposed.
 39. An axle assembly according to claim 37 where said axleshafts are rotatably supported in said housing structure and drivinglyconnected to said mechanical differential.
 40. An axle assemblyaccording to claim 37 wherein said bridging element includes between itsends an intermediate portion and where said intermediate portion isexposed exteriorly of said housing structure.
 41. An axle assemblyaccording to claim 37 wherein said bridging element further performs asa bearing to support said at least one shaft.
 42. An axle assemblyaccording to claim 37 and including a parking brake external to saidhousing structure and attached to said at least one shaft.
 43. An axleassembly according to claim 37 and including a fluid barrier disposedadjacent said bridging element in said housing structure to preventhydraulic fluid held within said first chamber from entering said secondchamber, a header tank disposed external to said housing structure andarranged to communicate with said first chamber, said header tankattached to said housing structure allowing the expansion andcontraction in the fluid volume held by said first chamber.